Traditional gas turbine combustors use non-premixed (“diffusion”) flames in which fuel and air freely enter a combustion chamber separately. However, the diffusion flames burn at such a high temperature that unacceptable levels of nitrogen oxide (NOx) are emitted.
One method used to lower NOx emissions includes using lean premixed combustion in which fuel and air are premixed in a premixer section, and the fuel-air mixture is injected into a combustion chamber where it is burned. Lean premixed combustion can result in low NOx emissions for very uniform fuel air mixtures, however, such mixtures are typically prone to combustion instability. This instability can be overcome by the presence of a pilot. However, typically a pilot results in excessive NOx formation, which therefore reduces the benefit of using the lean premixed combustion method.